1. Field of the Invention
This invention relates to an improved apparatus for forming a coating of rubber or a synthetic resin having an even thickness on the external surface of a tubular textile jacket. More particularly, this invention relates to the use of an expanding assembly provided with one or more expanding members in the method for forming a coating of rubber or a synthetic resin on the external surface of a tubular textile jacket, the expanding members being capable of inflating the tubular textile jacket circularly or elliptically in its cross section when packed thereinto and keeping the jacket inflated during the step of solidifying a coating liquid applied onto the external surface of the jacket by drying or vulcanization.
2. Description of the Prior Art
A method for forming a coating of rubber or a synthetic resin on the external surface of a tubular textile jacket is already disclosed in British Pat. No. 957,929 relating to improvements in the method of manufacturing fire hose which comprises forming a coating on the external surface of a hose jacket and turning it inside out. This patent discloses two methods for the first step of forming the coating on the external surface of a hose jacket. One method comprises passing a hose jacket in flattened state through a bath of a latex or plastisol and then vulcanizing or gelling the coating on the external surface of the hose jacket, while the other method comprises inserting an air-tight air bag into the interior space of the hose jacket, supplying air in the air bag to inflate the hose jacket, passing the inflated jacket as such through a bath of a latex or plastisol and then vulcanizing or gelling the coating on the external surface of the hose jacket.
These methods are the simplest ones for forming a coating on the external surface of a tubular textile jacket. However, these methods are complicated in practical operation and have a number of defects as will be detailed hereinafter. Thus, these methods make themselves unsuited for the manufacture of commercially valuable products having a uniform coating thereon.
In the firstly mentioned method wherein a hose jacket is passed in flattened state through a bath of a latex or plastisol, a difference in surface curvature is made between the flattened broad areas and the folded edge areas of the hose jacket and a significant difference in flow state is found between the liquid attached to the flattened broad areas and that attached to the folded edge areas; the quantity of liquid attached to the folded edge areas becomes smaller than that attached to the flattened broad areas, and as the result, a coating layer formed after solidification of the liquid becomes extremely thin in the folded edge areas. According to this method, therefore, a coating of an even thickness cannot be formed on the external surface of the hose jacket and two longitudinally extending lines where the coating is smaller in thickness will appear in the diametrically opposite positions of the resulting product. Such thinly coated areas in the hose jacket give a detrimental effect to the commercial value of the product and will tend to form pinholes when the hose jacket is subjected to further treatments including evagination, pressure test, etc. for manufacturing the desired fire hose. Such pinholes will prove fatal defect to fire hose. On the other hand, the external coating formed in the folded edge areas of the hose jacket is comparatively thin and most damageable by external force or friction. Thus, there is a fear of injury in such areas during the subsequent treatment for manufacturing fire hose. The firstly mentioned method thus fails to produce a coating of an even thickness and rather serves to minimize the merit achieved by forming a coating on the external surface of hose jacket.
In the secondly mentioned method wherein the formation of such external coating is conducted while the hose jacket is inflated by the aid of an air bag packed thereinto, no problem arises in the formation of an external coating having an even thickness unlike the firstly mentioned method. However, this method also has several serious drawbacks. In practice of this method, an air bag has to be inserted into the tubular textile jacket over the full length thereof and therefore some additional operations including insertion of an air bag into the interior of jacket, elevation of air pressure in the air bag and taking out of the air bag from the jacket after the formation of external coating are requird, thus making the procedure extremely complicated. Extremely difficult in the technical point of view for this method is to seal the air bag perfectly for preventing leakage of air therefrom. Even a slight leakage of air incurs shrinkage of the inflated hose jacket and finally results in the formation of a coating having uneven thickness. In this case, leaked air is released through voids in the reticulate structure of the fibrous jacket whereby a coating once formed is broken to cause the formation of pinholes or cracks on evagination of the hose jacket. Moreover, the hose jacket inflated according to this method by the aid of pressurized air bag is stiff and so is hardly curved. Thus, storage of the inflated hose jacket needs a considerably large space. If the inflated hose jacket is forcedly curved with a smaller radius of curvature, smooth curving will no longer be attained and the hose jacket will be curved with an angle in several positions. If the running course of inflated hose jacket is changed during the operation, rolls having a diameter of at least one meter will be needed to warrant smooth curving of the inflated jacket, thus resulting in considerable enlargement of the apparatus.
Accordingly, the secondly mentioned method is also commercially unattractive in every respect of space, apparatus and expenses and has complexity and difficulty in technical operations.
To overcome these serious defects in the prior arts, there was already proposed an improved method for forming a coating of rubber or a synthetic resin having an even thickness on the external surface of a tubular textile jacket (Japanese Pat. Appln. No. 58446/1972). This method, i.e. the improved prior method comprises packing into the interior space of a tubular textile jacket drawn upwardly from a bath of a coating liquid an expanding member capable of inflating the tubular jacket to almost circular form in its cross section, for example, a self-rotatable endless double tubing or steel balls and then maintaining the inflated jacket in a definite position to the bath of coating liquid thereby keeping the jacket inflated at least for a distance from the position where the tubular textile jacket departs from the bath of coating liquid to the position where the coating liquid attached to the external surface of the jacket becomes no longer fluid.
According to the improved prior method wherein such specific expanding member is used, a tubular textile jacket running in a bath of a coating liquid is kept almost circular in its cross-section and continuously kept in this state for a certain distance after drawn from the bath, whereby the flow state of the liquid attached to the external surface of the tubular jacket is maintained identical all over the external surface to permit the formation of a coating of an even thickness all over the external surface. Once the liquid attached to the external surface of a tubular textile jacket has been solidified to a certain degree to lose its fluidity, the running jacket may be flattened and turned at a roll with a smaller diameter. Thus, the improved prior method is advantageous in respect of space for treating the jacket and needs no troublesome operation for putting in and out the air bag.
This method is, therefore, superior to the methods disclosed in the aforementioned British patent but still has some shortcomings. Since an article (endless double-tubing) used in this method as the expanding member and inserted into the interior space of a tubular textile jacket may be regarded as one of the air bags, a somewhat troublesome operation is also required for perfectly sealing the endless double-tubing. The technical merit of the improved prior method over the British patent is that several hundred to several thousand tubular textile jackets can be treated according to this method with only one endless double-tubing, while one air bag is required for each one of the hose jackets according to the method of the British patent. Although this technical merit fully covers difficulty in perfectly sealing the endless double-tubing, further improvement is demanded in the operation for putting in and out the expanding member. In the improved prior method using the endless double-tubing, leakage of air or a fluid may also occur during the operation. In this case, sudden shrinkage of the inflated double-tubing takes place, thus resulting in the formation of a coating having uneven thickness as in the case of the British patent. In case the coating operation is carried out repeatedly with plural endless double-tubings by passing a tubular textile jacket continuously through a plurality of coating baths arranged in series, leakage of the content in one or two endless double-tubing may not incur serious damage to the product. However, such leakage phenomenon is quite undesirable in practice of the improved prior method and should be avoided. To overcome these defects in the improved prior method, therefore, there is still a great demand for development of an improved method for carrying out the coating operation without any trouble.